Toilet bowl cleaning tablet

ABSTRACT

A cleaning formulation, in tablet form, capable of providing a metered release of cleaning active while immersed in the tank of a toilet. The tablet comprises greater than about 85 to 99 weight percent of a halohydantoin plus about 1 to 15 weight percent of a longevity aid comprising boric acid.

This application claims the benefit of U.S. Provisional Application Ser.No. 60/005,969, filed Oct. 27, 1995.

FIELD OF THE INVENTION

This invention relates to formulations for cleaning toilet bowls, and inparticular to an in-tank toilet bowl tablet providing metered release ofan active cleaning agent.

BACKGROUND OF THE INVENTION

There are numerous compositions known to the art which can be compressedor tableted, providing a tablet, block or similar article which may beplaced in the tank of a toilet and dispense cleaning active over aperiod of time. Such tablets may consist of, or include various cleaningagents such as bleaches, surfactants, disinfectants, and mixturesthereof. A particularly preferred disinfecting agent is an organichalogen source, and a particularly preferred family of organic halogensources include halohydantoins. Halohydantoins are particularlypreferred for the purpose as they are well suited to tableting andconsequent slow release of halogen. Numerous prior art discloseshalohydantoin based cleaning tablets for various uses, including U.S.Pat. Nos. 4,427,692; 4,537,697 and 4,560,766, all to Girard.

One of the difficulties associated with toilet bowl cleaning tablets ofthe art has been to establish a uniform release of active halogen over acommercially feasible term, for example, of two to four months. Whiledichloro, methylethyl or dimethyl hydantoins can be compressedsufficiently to permit such a long term release, for reasons offormulation efficacy and economics, pure dichloro, methylethyl ordimethyl, or other halohydantoins are not preferred. However sufficienttablet longevity is hindered when such tablets are not purehalohydantoin.

Accordingly, it is an object of the present invention to provide acomposite tablet having longevity comparable to a pure halohydantointablet.

It is another object of the present invention to provide a compositetablet having cleaning performance comparable to that of a purehalohydantoin tablet.

SUMMARY OF THE INVENTION

The present invention is a cleaning formulation, in tablet form, capableof providing a metered release of cleaning active while immersed in thetank of a toilet.

In one aspect, the invention is directed to a cleaning tablet comprisinga halohydantoin and boric acid wherein the halohydantoin comprisesgreater than about 85% (wt) to about 99% (wt) of the cleaning tablet.

In another aspect, the invention is directed to a method of dispensinguniform amounts of active halogens into a reservoir containing about 6to 19 liters of water which is periodically flushed and replaced withfresh water which includes the steps of:

a. placing a cleaning tablet which comprises a halohydantoin and boricacid into said reservoir wherein the halohydantoin comprises greaterthan about 85% (wt) to about 99% (wt) of the cleaning tablet and whereinactive halogen is released from the tablet until the concentration ofactive halogens in the water is at a desired level of about 0.5 to 5ppm;

b. removing the water from the reservoir and replacing said reservoirwith fresh water thereby activating the release of the active halogenfrom the tablet until the concentrate of active halogens in the waterreaches said desired level; and

c. repeating step b until the tablet is essentially completelydissolved, wherein the method is characterized in that the boric acidhas a dissolution time of about 0.08 to 0.3 of the total tabletdissolution time.

Preferred halohydantoins are selected from the group consisting ofN,N'-dichloro-dimethyl-hydantoin, N-bromo-N-chloro-dimethyl-hydantoin,N,N'-dibromo-dimethyl-hydantoin, 1,4dichloro, 5,5-dialkyl substitutedhydantoin, wherein each alkyl group independently has 1 to about 2carbon atoms, and mixtures thereof.

Preferably, the cleaning tablet has a density of about 1.1 to 1.6 g/cm³.In addition, the cleaning tablet has a superficial surface area toweight ratio of about 1:1 to 2:1 (cm² /g).

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph of tablet dissolution rate for various ratios ofhydantoin to boric acid.

DETAILED DESCRIPTION OF THE INVENTION

The toilet cleaning tablet or block of the present invention is agenerally homogenous solid comprising an active halogen-releasing agentand a longevity aid. The halogen releasing agent releases the halogenwhen the block is in contact with water. Any such agents knownheretofore can be used and it is preferred that such agents areN-halogenated organic compounds, includingN,N'-dichloro-dimethyl-hydantoin, N-bromo-N-chloro-dimethyl-hydantoin,N,N'-dibromo-dimethyl-hydantoin. In the present invention, dialkylsubstituted hydantoins and especially 1,4dihalo, 5,5-dialkyl substitutedhydantoins, are preferred. Preferred is a mixture of bromochlorodimethyl hydantoin (BCDMH), dichloro dimethyl hydantoin (DCDMH), anddichloro methyl ethyl hydantoin (DCMEH). For tableting purposes, DCDMHis preferred as it provides the longest residence time. Thesehalohydantoins are available from Lonza Chemical, Fairlawn, N.J.Preferably the halohydantoins comprise greater than about 85% (wt) toabout 99% (wt) of the cleaning block, preferably about 90% (wt) to about99% (wt), with the remainder comprising boric acid. Preferred tabletscan comprise from about 5% (wt) to less than 15% (wt), preferably fromabout 7.5% (wt) to about 12.5% (wt), and more preferably from about 8%(wt) to about 12% (wt) of the boric acid.

It is known that solid halo-5,5-dialkyl substituted hydantoins dissolveslowly in water. Surprisingly, it was discovered that if a quantity of aboric acid longevity aid was added to the hydantoin mixture within arange of between about 5 and 10% based on the weight of the toiletcleaning block, and if the block was prepared such that it had a densityfalling within a particular range, namely 1.1 to 1.6 g/cm³ and also ifthe ratio of superficial surface area (cm²) to weight (grams) fellwithin a certain range, namely about 1:1 (cm² /g) to 2:1 (cm² /g), thetoilet cleaning block would release a controlled, substantially constantamount of halogen disinfecting agent within the range of 0.5-5 ppm overa period of 2 to about 4 months of constant contact with water. Thetablet longevity aid must be water soluble, chemically inert, i.e. willhave no effect on the solubility of the halohydantoin or halohydantoinmixture, and will completely dissolve in a much shorter time period thanthe halohydantoin. Preferably, the dissolution time for the longevityaid should be approximately 0.08 to 0.3, more preferably 0.1 to 0.15, ofthe dissolution time for the overall or total tablet. Statedalternatively, the longevity aid should completely dissolve inapproximately 1-4 weeks, preferably 2-3 weeks, for a hydantoin tablethaving an approximately 4 month longevity. Optionally compatibleadjuncts such as colorants such as dyes, surfactants antimicrobialagents and fragrances may be added to the formulation subject only tothe limitation that such adjuncts have substantially no effect on tabletdissolution rate. Although adjuncts can be included, preferredembodiments include tablets that consist essentially of thehalohydantoin and basic boric acid.

The block will deliver a constant, uniform efficacious level of activehalogen (0.5 to 5 ppm) for about 1000-2000 flushes with water having atemperature of about 50° to 70° F. (10° to 21° C.) and typically about57° F. (13.9° C.) and will be completely dissolved at the end of itsuseful life, leaving no residue in the tank. A tank will typically holdabout 3.5 gallons (about 13.2 liters) of water, although tank sizesvary, they typically have a capacity that ranges from about 6 to 19liters. For household applications, the tablet preferably has a mass ofat least about 25 grams and more preferably about 50-100 grams.

An important relationship between tablet surface area and tablet volumehas been discovered. It has been found that with respect to dissolutionof substantially pure halohydantoin tablets, there is a "superficial"surface area which is defined by the exterior topography of the tabletand does not include the interior surface area of the tablet. By"superficial" surface area is meant the geometric or exterior surface ofthe tablet and not its true surface area. For instance, if the tablet iscube-shaped, then the superficial surface area is calculated as 6×s₂,where s is the length of one side of the cube. It is the ratio of tabletsuperficial surface area (cm²) to tablet weight (grams) which isimportant in tablet longevity. The lower the ratio the greater thelongevity, and the higher the ratio the shorter the longevity. It hasbeen experimentally determined that a preferred ratio be between about1:2 to 2:1 (cm² /g) and more preferably about 1.2:1 to 1.3:1 (cm² /g).Without intending to be bound by theory, it is the thought that when ahalohydantoin tablet is exposed to water the tablet tends to "cement"together due to water of hydration and hydrogen bonding betweenparticles of the organic bleach. Thus, when exposed to water thehalohydantoin forms a matrix that dictates the superficial surface area.

The toilet cleaning tablet of the present invention is prepared by drymixing the hydantoin and the boric acid, preferably in finely dividedform, and an optional internal mold lubricant in the absence of addedwater. Any adjunct materials are also added to the blend. An externallubricant may be used in the manufacturing process to help release theblock from the mold. Any type of mixer such as a twin-shell, ribbonblender or similar type of mixer that is designed to provide ahomogeneous admixture can be used. The particle size of thehalohydantoin is preferably in the range of 10 to 60 US mesh and that ofthe boric acid is preferably in the range of 8 to 100 US mesh. Theadmixture is then transferred to the mold of a press, and pressure isapplied sufficient to provide the desired density and effective surfacearea/weight ratio. The resultant mixture is a coherent solid which isresistant to internal water penetration and has a crush fracturingstrength of about 25 to 100 pounds, preferably about 50 to 80 pounds.The strength was measured using an AMETEK force gauge testing devicemanufactured by the AMETEK Corporation. In order to obtain the desiredproperties, the pressure will vary depending on the particular chemicalsemployed and the particle sizes of the particulates.

EXPERIMENTAL

Without being bound to any particular theory, it has been demonstratedthat adding up to about 10% boric acid is feasible without affecting theinternal matrix structure that occurs when using 100% halohydantoin. Thedata also suggests that it may be feasible to use up to almost 15% boricacid. The more soluble boric acid will rapidly dissolve from the tabletleaving a remaining "matrix" of the halohydantoin. The result is thatthe dissolution behavior of the preferred composite tablet is verysimilar to that of a pure halohydantoin tablet due to similar matrices,yielding similar superficial surface to volume ratios.

As shown in FIG. 1 and in Table 1 below, a 15% boric acid tablet resultsin a loss of about 6 to 10% longevity, due to the different superficialsurface area to weight ratios versus the control (100% halohydantoin).If the boric acid is increased beyond 15% the kinetics of tabletdissolution can be shown to markedly shorten tablet longevity. FIG. 1 isa graph showing the log of percentage tablet remaining versus time(weeks) for two formulations of the present invention (5% and 10% boricacid) three formulations outside the present invention (15, 20 and 30%boric acid) and a 0% boric acid control. In each case, the tabletcomprises halohydantoin plus the indicated level of boric acid. Thetablets had a superficial surface area to weight ratio of about 1.25:1(cm² /g). The data presented graphically in FIG. 1 is shown in Table 1below.

                  TABLE 1                                                         ______________________________________                                        PERCENTAGE TABLET REMAINING                                                   Tablet    Time (Weeks)                                                        Composition                                                                             1        2      3       4    5                                      ______________________________________                                        A         86.5     71.8   59.7    48.9 37.7                                   B                  85.9                                                                           71.1    59.0    48.4                                                                              37.8                                  C                  83.4                                                                           67.1    54.4    43.5                                                                              32.4                                  D                  81.0                                                                           63.3    49.7    38.8                                                                              27.3                                  E                  75.8                                                                           53.9    38.4    24.4                                                                              12.1                                  F                  89.5                                                                           75.3    61.9    50.3                                                                              38.4                                  ______________________________________                                         A = 5% Boric Acid                                                             B = 10% Boric Acid                                                            C = 15% Boric Acid                                                            D = 20% Boric Acid                                                            E = 30% Boric Acid                                                            F = 0% Boric Acid                                                        

The data from Table 1 above were obtained using the following protocol.Tablets each weighing 70 grams were compressed from appropriate amountsof halohydantoin and boric acid, on a Carver hand press usingconventional tablet tooling consisting of a die and an upper and lowerpunch. The resulting tablets measured about 5.0 cm in diameter and about2.2 cm in height. The experimental tablets were placed in toilet tanksand flushed three to five times daily. The water temperature wasmaintained at about 70° (21° C.) to 75° F. (24° C.) for the duration ofthe test. The tablets were checked daily for weight loss, which data wasused to evaluate the longevity of the tablets.

The foregoing has described the principles, preferred embodiments andmodes of operation of the present invention. However, the inventionshould not be construed as limited to the particular embodimentsdiscussed. Instead, the above-described embodiments should be regardedas illustrative rather than restrictive, and it should be appreciatedthat variations may be made in those embodiments by workers skilled inthe art without departing from the scope of the present invention asdefined by the following claims.

What is claimed is:
 1. A cleaning tablet consisting of a halohydantoinand boric acid wherein the boric acid is present in amounts from 7.5% wtto 15% wt of the cleaning tablet and wherein the tablet has a density ofabout 1.1 to 1.6 g/cm³ and the tablet has a superficial surface area toweight ratio of about 1:1 to 2:1 cm² /g.
 2. The cleaning tablet of claim1 wherein the halohydantoin is selected from the group consisting ofN,N'-dichloro-dimethyl-hydantoin, N-bromo-N-chloro-dimethyl-hydantoin,N,N'-dibromo-dimethyl-hydantoin, 1,4dichloro,5,5-dialkyl substitutedhydantoin, wherein each alkyl group independently has 1 to about 2carbon atoms, and mixtures thereof.
 3. The cleaning tablet of claim 1wherein the boric acid is present in amounts from 10% wt to 15% wt ofthe cleaning tablet.
 4. The cleaning tablet of claim 1 wherein thetablet has a mass of at least 25 grams.
 5. A method of dispensinguniform amounts of active halogens into a reservoir containing about 6to 19 liters of water which is periodically flushed and replaced withfresh water which comprises the steps of:a. placing a cleaning tabletwhich consists of a halohydantoin and boric acid into said reservoirwherein the boric acid is present in amounts from 7.5% wt to 15% wt ofthe cleaning tablet and wherein active halogen is released from thetablet until the concentration of active halogens in the water is at adesired level of about 0.5 to 5 ppm wherein the tablet has a density ofabout 1.1 to 1.6 g/cm³ and the tablet has a superficial surface area toweight ratio of about 1:1 to 2:1 cm² /g; b. removing the water from thereservoir and replacing said reservoir with fresh water therebyactivating the release of the active halogen from the tablet until theconcentrate of active halogens in the water reaches said desired level;and c. repeating step b until the tablet is essentially completelydissolved, wherein the method is characterized in that the boric acidhas a dissolution time of about 0.08 to 0.3 of the dissolution time ofthe total tablet, wherein said method is characterized by being able toprovide said desired level of active halogens when step b is repeatedbetween 1,000 to 2,000 times and when the water temperature ismaintained at about 10° C. to 21° C.
 6. The method of claim 5 whereinthe boric acid is present in amounts from 10% wt to 15% wt of thetablet.
 7. The method of claim 5 wherein the tablet has a mass of atleast about 25 grams.
 8. A cleaning tablet consisting of ahalohydantoin, boric acid and a compatible adjunct that is selected fromthe group consisting of colorants, surfactant, antimicrobial agents, andfragrances wherein the halohydantoin is greater than 85% wt, the boricacid is present in amounts from 7.5% wt to 15% wt of the cleaning tabletand wherein the tablet has a density of about 1.1 to 1.6 g/cm³ and thetablet has a superficial surface area to weight ratio of about 1:1 to2:1 cm² /g.
 9. The cleaning tablet of claim 8 wherein the halohydantoinis selected from the group consisting ofN,N'-dichloro-dimethyl-hydantoin, N-bromo-N-chloro-dimethyl-hydantoin,N,N'-dibromo-dimethyl-hydantoin, 1,4dichloro, 5,5-dialkyl substitutedhydantoin, wherein each alkyl group independently has 1 to about 2carbon atoms, and mixtures thereof.
 10. The cleaning tablet of claim 8wherein the boric acid is present in amounts from 10% wt to 15% wt ofthe cleaning tablet.
 11. The cleaning tablet of claim 8 wherein thetablet has a superficial surface area to weight ratio of about 1.2:1 to1.3:1 cm² /g.
 12. A method of dispensing uniform amounts of activehalogens into a reservoir containing about 6 to 19 liters of water whichis periodically flushed and replaced with fresh water which comprisesthe steps of:a. placing a cleaning tablet which consists of ahalohydantoin, boric acid, and a compatible adjunct that is selectedfrom the group consisting of colorants, surfactant, antimicrobialagents, and fragrances into said reservoir wherein the halohydantoin isgreater than 85% wt, the boric acid is present in amounts from 7.5% wtto 15% wt of the cleaning tablet and wherein active halogen is releasedfrom the tablet until the concentration of active halogens in the wateris at a desired level of about 0.5 to 5 ppm wherein the tablet has adensity of about 1.1 to 1.6 g/cm³ and the tablet has a superficialsurface area to weight ratio of about 1:1 to 2:1 cm² /g; b. removing thewater from the reservoir and replacing said reservoir with fresh waterthereby activating the release of the active halogen from the tabletuntil the concentrate of active halogens in the water reaches saiddesired level; and c. repeating step b until the tablet is essentiallycompletely dissolved, wherein the method is characterized in that theboric acid has a dissolution time of about 0.08 to 0.3 of thedissolution time of the total tablet, wherein said method ischaracterized by being able to provide said desired level of activehalogens when step b is repeated between 1,000 to 2,000 times and whenthe water temperature is maintained at about 10° C. to 21° C.
 13. Themethod of claim 12 wherein the boric acid is present in amounts from 10%to 15% wt of the tablet.
 14. The method of claim 12 wherein the tablethas a mass of at least about 25 grams.